Iron is an essential nutrient for virtually every organism on the earth yet it is also a potent cellular toxin. Both iron deficiency and iron overload contribute to diseases in humans. Hereditary hemochromatosis is a genetic disorder caused by excess uptake of iron from the diet, resulting in multi-organ failure and, often, liver cancer. Chronic viral hepatitis and other inflammatory diseases of the liver are frequently associated with hepatic iron overload and the neurodegenerative diseases also are associated with iron deposition in affected areas of the brain. The molecular events that lead to iron accumulation and the processes through which iron causes damage to cells are largely unknown.Our research involves the use of whole-genome approaches to identify genes that are involved in iron metabolism in the budding yeast, Saccharomyces cerevisiae. We have employed DNA microarray analysis of the entire yeast genome to identify genes that are regulated at the transcriptional level by changes in iron availability. Many previously identified genes and several uncharacterized genes were identified as the regulon of genes controlled by the major iron-dependent transcription factor, AFT1. Using available genome and protein databases, these newly identified genes have been grouped into families and experiments are underway to evaluate the functions of these genesOur studies of these newly identified genes have uncovered a novel pathway of siderophore-mediated iron uptake in yeast and we have identified four homologous siderophore transporters, including the transporter for the therapeutic iron chelator desferrioxamine. Our data indicate that siderophore-mediated iron uptake occurs through two genetically separable, parallel pathways, one of which is located on the plasma membrane and one that is intracellular. We have also determined that iron availablility can affect both nitrogen utilization pathways and purine metabolism pathways; the mechanism of this regulation is being studied. These data were presented at the 2000 Yeast Genetics and Molecular Biology meeting and the annual meeting of the American Society for Cell Biology as well as in seminars at Georgetown University, the University of Utah, and on the NIH campus. Using this approach we hope to identify mammalian homologues of these proteins, and to define pathways of iron uptake, utilization, and detoxification in humans. This work will enable the design of rational therapeutic or preventative treatments for patients susceptible to iron overload.